1. Field of the Invention
The present invention relates to a variable capacity swash plate type compressor suitable for use as a refrigerant compressor for an air conditioning system for a vehicle.
2. Description of the Related Art
As a variable capacity swash plate type compressor there is known a double-headed plunger type compressor in which compression chambers are formed on both sides of reciprocating plungers to thereby conduct a fluid pumping cycle twice for every one reciprocation of the plunger.
FIG. 4 shows an example of the variable capacity swash plate type compressor using such double-headed plungers.
As shown in FIG. 4, a variable inclination rotary swash plate 207 is installed on and is rotated together with a drive shaft 201. The swash plate 207 is also slidably engaged with plungers 209 at the periphery thereof, via sliding shoes 216 and 219. When the swash plate 207 is rotated together with the drive shaft 201, it is also swung back and forth around an axis perpendicular to the drive shaft, to thereby reciprocate the plungers 209 in a direction parallel to the axis of the drive shaft 201. This reciprocation of the plungers causes the fluid to be compressed to be drawn into compression chambers 250, 251 disposed on both ends of the plungers 209, and then the fluid is compressed therein and discharged therefrom.
In the compressor of FIG. 4, the capacity of the compressor is controlled by adjusting a pressure in a control pressure chamber 200, formed on a rear side of a control piston 230, by using a pressure regulating valve 300. Namely, by changing the pressure acting on the rear side of the piston 230, the piston 230 is moved along the drive shaft 201, and accordingly, the axial position of the swash plate 207 is changed in accordance with the change of position of the piston 230.
The swash plate 207 is connected to the drive shaft 201 by a coupling formed by a flat position 265 of the drive shaft 201 and flat plates 270 on the swash plate 207. Namely, a part of the drive shaft 201 has a flat plate shape 265. Also, two flat plates 270 are projected vertically from the swash plate and form a slit therebetween. An elongated hole 266 is formed on the flat portion 265 of the drive shaft. The drive shaft 201 and the swash plate are coupled by inserting said flat portion 265 of the drive shaft into the slit formed between flat plates 270 of the swash plate 207, whereby the rotating torque is transmitted from the drive shaft 201 to the swash plate 207 through the contact between the flat portion 265 and the flat plates 270. The angle of inclination of the swash plate 207 is controlled by a pin 265 fitted to the flat plates 270 of the swash plate 207 and cooperating with the elongated hole 266.
Namely, when the swash plate 207 is moved axially by the piston 230, the pin 280 slides in the elongated hole 266, and the angle of inclination of the swash plate is changed in accordance with the axial position of the swash plate. The shape and position of the elongated hole 266 is determined such that the angle of inclination of the swash plates is changed to maintain the top dead center of the plunger at the side of the compression chamber 250 at a substantially constant position when the axial position of the swash plate is changed.
By this arrangement, the position of the top dead center of the plunger at compression chamber 250 remains substantially the same when the stroke of the plunger i.e., the capacity of the compressor, is changed.
Since the compression chambers can be formed on both sides of the plungers, the double-headed type plungers are advantageous for an enlarging of the capacity of the swash plate type compressors, and consequently, the variable capacity swash plate type compressors using double-headed type plungers are suitable for use for the air conditioning system of larger size vehicles.
Recently, however, the air conditioning systems have become also commonly used for smaller size vehicles, and in the air conditioning systems for smaller size vehicles, the variable capacity compressors are required to have a smaller size and capacity.
To reduce the size and the capacity of the swash plate type compressor, single-headed plungers having compression chambers formed on one side thereof only are used. Namely, in the variable capacity compressors using the single-headed plungers, usually the capacity of the compressor can be controlled by adjusting the pressure in the crank chamber, and therefore, the provision of the control pressure chamber 200 and the piston 230 shown in FIG. 4 can be eliminated, to thereby achieve a reduction of the size of the compressor. Further, since the compression chambers are formed on only one end, the force biasing the single-headed plunger and the swash plate towards the compression chambers can be controlled by adjusting the pressure in the crank chamber (i.e., the pressure exerted on the rearside of the plunger). Therefore, the stroke of the plunger can be controlled by adjusting the axial position and the angle of inclination of the swash plate in accordance with that biasing force, using a pin (280) and an elongated guide hole (266) arrangement similar to that shown in FIG. 4.
Nevertheless, several problems have arose in the variable capacity swash plate type compressors using single headed plungers.
For example, because of the large volume of the crank chamber, a longer time is required to adjust the pressure in the crank chamber to a desired value, and therefore, the response of the capacity control is slower.
Also the pressure in the crank chamber cannot be arbitrarily set, due to the limitations imposed by the reaction force on the plunger, the friction force of the parts, and the strength of the spring, etc., and therefore, the pressure in the crank chamber usually can be adjusted only within a small range close to the suction pressure of the compressor. This further worsens the response and the accuracy of the capacity control.
Also, the conventional double-headed plunger is in contact with the wall of the compression chamber at the peripheries of both ends of the plunger. Therefore, the moment transferred from the swash plate, which acts to incline the plungers, can be received at both ends of the plunger, whereby a large span between the load bearing points is obtained to reduce a radial load caused by the moment transferred from the swash plate.
In the case of the single-headed plunger, however, the compression chamber is formed on only one side of the plunger, and consequently, the load caused by the moment transferred from the swash plate is received by this end of the plungers only. This imposes a larger radial load on the sliding surface of the cylinder bores and the plungers, and accordingly, reduces the durability of these parts against wear.